1. Field of the Invention
The present invention relates to a lens driving apparatus for a disk player which optically writes/reads information to/from a disk-shaped recording medium such as a compact disk or an optical disk.
2. Description of Related Art
Conventionally, a lens driving apparatus 1 for a disk player for reproducing information recorded on an optical disk such as a CD or a DVD has been known. In order to read information recorded on an optical disk accurately, the lens driving apparatus 1 for a disk player performs a focus control for controlling a distance between an information recorded surface of the optical disk and an objective lens with respect to warping or deflection of the optical disk, and a tracking control for follow-up controlling the objective lens with respect to the eccentricity of an information track of the optical disk. The structure of the lens driving apparatus 1 for a disk player will be described with reference to FIG. 1.
A pick-up device 1 comprises: a plate-shaped actuator base 4 including yokes 3 provided so as to be opposed to each other to which a pair of magnets 2 are fixed respectively; a movable portion 7 which is movably supported, via four supporting wires 6a-6d, by a supporting base 5 which is fixed to a side surface of the actuator base 4 by, e.g., a screw (not shown); a box-shaped actuator cover 14 for protecting the movable portion 7, which is made of a metal plate or a resin and which includes an opening hole 14A for an objective lens 8 in a top portion thereof; and a pick-up body (not shown) for containing optical components such as a light source, a collimator lens, and a beam splitter. The movable portion 7 comprises: a lens holder 10 containing the objective lens 8 and having four fixed arms 9 which protrude in tracking directions; a focus coil 11 wound around the body of the lens holder 10; and four D-shaped tracking coils 12 which are fixed to the respective side surfaces of the lens holder 10 respectively opposing to the magnets 2. The movable portion 7 is supported to be movable with respect to the actuator base 4 by providing the four fixed arms 9 of the lens holder 10 in the supporting base 5 and fixing the four fixed arms 9 to the four supporting wires 6a-6d. 
The four supporting wires 6a-6d are used to movably support the movable portion 7 and used also as a connecting line for supplying a driving current to the focus coil 11 and the four tracking coils 12. Therefore, each of the four supporting wires 6a-6d is made of an elastic member with a high conductivity.
One end of the focus coil 11 wound around the body of the lens holder 10 is connected to, for example, the supporting wire 6a, and the other end of the focus coil 11 is connected to the supporting wire 6b. Thus, by supplying a focus driving current to the two supporting wires 6a and 6b of the supporting base 5, the movable portion 7 is driven in a focus direction.
The four tracking coils 12 which are fixed to the respective side surfaces of the lens holder 10 are serially connected by using the two supporting wires 6c and 6d and a wiring member 13. More specifically, one supporting wire 6c is connected to a line end of one of the two tracking coils 12 which are fixed to one side surface of the lens holder 10 and which are serially connected with each other, and the other supporting wire 6d is connected to a line end of one of the two tracking coils 12 which are fixed to the other side surface of the lens holder 10 and which are serially connected with each other. The line ends of the other tracking coils 12 are connected with each other by the wiring member 13. Thus, the four tracking coils 12 are serially connected with respect to the two supporting wires 6c and 6d. Therefore, by supplying a tracking driving current to the two supporting wires 6c and 6d, the movable portion 7 is driven in a tracking direction.
The movable portion 7 of the pick-up device 1 is movably supported by the four supporting wires 6 as described above. Therefore, when the movable portion 7 receives a strong vibration, for example, it may move by a large distance in a focus direction, so that the objective lens 9 hits the information recorded surface of the optical disk, thereby scratching the information recorded surface. Thus, the pick-up device 1 regulates a movement in a focus direction generally by providing the actuator cover 14.
In recent years, along with the spread of high double-speed reproduction in an optical disk driving apparatus, there has been an increased need for a higher driving force of a spindle motor, i.e., an increase in the size of the spindle motor. As illustrated in FIGS. 2A and 2B, the optical disk driving apparatus comprises a turntable 16 axially supported on a spindle motor 15, and a conveying mechanism 18 for moving the pick-up device 1 in a radial direction (a direction indicated by K in the figure) of an optical disk 17. The conveying mechanism 18 comprises: a shaft 20 for slidably supporting a pick-up body 19 on which the lens driving apparatus 1 for a disk player is mounted in the radial direction of the optical disk 17; a rack 21 axially supported on the shaft 20; and a transmission gear 22 axially supported on a thread motor (not shown). In the pick-up body 19 on which the pick-up device 1 is mounted, the transmission gear 22 rotates along with the rotation of the thread motor, and the rotation of the transmission gear 22 is transmitted to the rack 21. Along with the rotation of the shaft 20, the pick-up body 19 moves in the radial direction of the optical disk 17.
The pick-up body 19 on which the pick-up device 1 is mounted is conveyed in an inner circumferential direction of the optical disk 17 by the conveying mechanism 18. However, as shown in FIG. 2B, the pick-up body 19 cannot move beyond a position where it contacts the spindle motor 15. On the other hand, the pick-up device 1 cannot move beyond a position where the actuator cover 14 contacts the turntable 16. As described above, along with the spread of high double-speed reproduction in an optical disk driving apparatus, the spindle motor has been required to have a higher driving force, and the size thereof has been increasing. As a result, such an extra space that the pick-up device can approach below the turntable is diminished, thereby making it difficult to read the innermost circumference of a disk.
The present invention has been made in view of the above-described problem, and an object thereof is to provide a lens driving apparatus for a disk player, which can easily approach to the innermost circumference of a disk and which can realize a reduction in size and weight thereof.
In order to solve the above-described problem, a lens driving apparatus for a disk player according to the first aspect of the present invention has such a structure that a lens holder including an objective lens, focus coils, and tracking coils fixed thereto is supported by a plurality of cantilevered wire-form elastic members, and drives the lens holder in focus and tracking directions. The wire-form elastic members include inner circumferential side wire-form elastic members and outer circumferential side wire-form elastic members which are disposed to be apart from each other in the tracking direction so as to interpose therebetween a point of application of a focus driving force generated from the focus coils. The inner circumferential side wire-form elastic members and the outer circumferential side wire-form elastic members have respectively different spring constants when deflected in the focus direction, and have respectively different distances to the point of application in the tracking direction.
A lens driving apparatus for a disk player according to the second aspect of the present invention is the lens driving apparatus for a disk player according to the first aspect of the present invention in which the spring constant of the inner circumferential side wire-form elastic members is greater than the spring constant of the outer circumferential side wire-form elastic members, and the distance from the inner circumferential side wire-form elastic members to the point of application is smaller than the distance from the outer circumferential side wire-form elastic members to the point of application.
A lens driving apparatus for a disk player according to the third aspect of the present invention is the lens driving apparatus for a disk player according to the first aspect of the present invention in which the spring constants of the inner circumferential side wire-form elastic members and the outer circumferential side wire-form elastic members, and the distances to the point of application have a relationship of FiTi=FoTo (wherein: Fi is the spring constant of the inner circumferential side wire-form elastic members; Ti is the distance from the inner circumferential side wire-form elastic members to the point of application; Fo is the spring constant of the outer circumferential side wire-form elastic members; and To is the distance from the outer circumferential side wire-form elastic members to the point of application).
A lens driving apparatus for a disk player according to the fourth aspect of the present invention is the lens driving apparatus for a disk player according to one of first to third aspects of the present invention in which the inner circumferential side wire-form elastic members and the outer circumferential side wire-form elastic members are formed by plate springs having the same thickness in the focus direction, and a width of each of the inner circumferential side wire-form elastic members in the tracking direction is greater than a width of each of the outer circumferential side wire-form elastic members in the tracking direction.
A lens driving apparatus for a disk player according to the fifth aspect of the present invention has a lens holder including an objective lens, focus coils, and tracking coils fixed thereto which is supported by a plurality of cantilevered wire-form elastic members, and drives the lens holder in focus and tracking directions. The wire-form elastic members include upper side wire-form elastic members and lower side wire-form elastic members which are disposed to be apart from each other in the focus direction so as to interpose therebetween a point of application of a tracking driving force generated from the tracking coils, and the upper side wire-form elastic members and the lower side wire-form elastic members have respectively different spring constants when deflected in the tracking direction, and have respectively different distances to the point of application in the focus direction.